Required operating procedure for turbines includes periodic operational testing (closing and reopening) of parallel inlet flow control valves used in turbines. The testing is done to confirm operability of turbine safety mechanisms. One problem with such testing is changes in the turbine steam boiler pressure or changes in turbine power as a result of the closing and reopening of the turbine control valves during the periodic operational test. Steam boiler pressure changes or turbine power changes must be minimized during turbine control valve operational safety test stroking. When present, the turbine inlet pressure regulation or turbine power feedback must not be affected or modified to achieve the compensation.
One pre-existing method to minimize inlet pressure excursions uses turbine inlet pressure in a proportional regulator. The inlet pressure regulator design is defined and required by the steam boiler design and, thus, cannot be modified. Other methods that have been used to compensate for turbine power disturbances caused by flow changes that occur during operational testing of inlet control valves are the use of electrical power feedback in a proportional plus integral regulator, or the use of turbine-stage pressure feedback in a proportional regulator. Neither of these methods may be applied to the inlet pressure problem because they both allow inlet pressure to change. Some of these methods also involve the monitoring of additional process parameters.